1. Field of the Invention
The present invention relates to a method for machining a slide core hole and a measurement/correction system for use in machining of a slide core hole, and more particularly to a technique for machining with a five-axis machine tool an inclined slide core hole for an extrusion pin in a mold for use in molding of a large-sized resin product, such as an instrumental panel or a bumper of an automobile.
2. Background Art
A bridge-type machine tool is conventionally known as a typical five-axis machine tool. A bridge-type machine tool includes a spindle head provided on a cross rail and has, in addition to X-axis, Y-axis and Z-axis, an A-axis for pivoting of the spindle head and a C-axis for indexing of a table. An example of such a bridge-type machine tool is disclosed in Japanese Patent Laid-Open Publication No. 2004-34168. Five-axis machine tools, including the bridge-type machine tool, have been advantageously used for machining of a free-form surface, as typified by machining of a propeller.
These days, the environment surrounding manufacturing industry is changing greatly, and demands by users are also changing. For example, shaping machining of a free-form surface as in value-added machining of a mold has conventionally been the highest priority, and high-speed rotation of a spindle and high-speed following in axial movement have previously been required. To meet the requirements, higher-speed and higher-precision shaping machining with a five-axis machine tool has become realized.
In these days, however, there is a stronger demand by users for a five-axis machine tool that can better perform process-intensive combined machining. While a significant improvement in high-speed, high-precision machining has been achieved as described above, old-fashioned machining operations are still practiced, and the imbalance is becoming a problem.
For example, in machining of a mold for molding a large-sized resin product, such as an instrumental panel or a bumper of an automobile, besides advanced shaping machining, there are many machining operations for which advanced shaping machining is not necessarily required, such as machining of a slide core hole for insertion of an extrusion pin, machining of a cooling cavity, undercut-shaping machining, etc.
Even today when high-speed machining is well-established, machining operations which are in no way high-speed and high-precision machining, such as machining of a slide core hole, are currently practiced in a labor-intensive manner by skilled workers. This is because a number of extrusion pin holes are provided in a mold, and the respective pin holes differ in inclination and azimuth. This is also because an extrusion pin is comprised of an insert portion, to be in contact with a product, and a rod portion, and in conformity with that, a slide core hole is comprised of a combination of two holes which differ in shape and depth, i.e., a core pocket in which the insert is to be housed and a rod hole in which the rod slides.
At present, when machining a slide core hole, machining of a core pocket and machining of a rod hole are generally carried out in separate steps. This often causes a phase misalignment between the core pocket and the rod hole, resulting in poor fitting of an insert into the core pocket. In such a case, machining to correct the core pocket for adjustment of the fitting is practiced manually.
While a core pocket and a rod hole can be machined by utilizing the high-speed cutting performance of a machine tool, an inefficient manual work is forced to be carried out for adjustment of the fitting at the final finish stage. This poses the significant problem that the high-speed cutting performance of a machine tool in shaping machining does not lead to enhanced machining efficiency.